Accelerator composition

ABSTRACT

Accelerator compositions having high activity which inhibit surface bloom in vulcanizates are comprised of a mixture of a thiourea of the structure II. a polysulfide of the structure III. tetramethyl thiuram disulfide or a mixture thereof with bis-(oxydiethylene)thiuram disulfide, or   V. the zinc salt of the reaction product of ethanolamine, formaldehyde and carbon disulfide.

Unite States atet Yochum et al. 1 July 4, 1972 [54] ACCELERATOR COMPOSITION [57] ABSTRACT [72] enters Daniel William Yochum Merchamvme Accelerator compositions having high activity which inhibit N J Paul Gordon aim; Lafayette f surface bloom in vulcanizates are comprised of a mixture of a a 9 a Ivan C. Popoff, Ambler, both of Pa. thlourea of the Structure [73] Assignee: Pennwalt Corporation, Philadelphia, Pa. S [22] Filed: 1971 111m s cumniixncn, s CNR u 21 Appl. No.: 116,250 with Il. a polysulfide of the structure [52] U.S. Cl ..252/182, 252/431, 252/426, 260/794 j =5 [51] Int. Cl ..C08c 11/48 imNcscnzsmmsiwmm [58] Field ofSearch ..252/l82,4l0,436 N,426, 431 P; or

260/794, 79.5 Ill. tetramethyl thiuram disulfide or a mixture thereof with References Clted bis-(oxydiethylene)thiuram disulfide, or

UNITED STATES PATENTS St. Albans et al ..260/79.5

Primary Examiner-John D. Welsh Attorney-Stanley Litz and Carl A. l-lechmer, Jr.

V. the zinc salt of the reaction product of ethanolamine, formaldehyde and carbon disulfide.

IV. ROS (W 5 Claims, No Drawings ACCELERATOR COMPOSITION This invention relates to compositions which are active accelerators for the vulcanization of elastomers, and more particularly to an accelerator composition comprising a mixture of a particular thiourea with another sulfur-containing compound, which mixture is especially useful in retarding surface bloom in vulcanized elastomers, especially in elastomeric terpolymers of ethylene, propylene and a diene monomer.

In the process of vulcanization of elastomers using an accelerator with sulfur or other vulcanization agent, there has been a need for a non-blooming type of accelerator that has adequate accelerator activity. The thiurams, such as tetramethyl thiuram disulfide and tetraethyl thiuram disulfide, have high activity as accelerators but they give an undesirable surface bloom on elastomer vulcanizates. Surface bloom is an undesirable phenomenon characterized by the appearance of a coating of solids or oil upon the surface of a vulcanizate as a result of the migration to the surface of one or more of the components of the vulcanized elastomer. This may occur quickly, as for example, in a few days, or not until several months have elapsed. It is particularly a problem in the case of EPDM elastomers, which are terpolymers of ethylene, propylene and a diene monomer, for example, ll-ethyl-l lltridecadiene, 1,5-cyc1ooctadiene, 1,4-hexadiene, S-ethylidene-2-norbornene, -methylene-2-norbornene, dicyclopentadiene, 2,5-norbornadiene and the like. Moreover, the curing of the EPDM elastomer requires a high activity accelerator because of the low level of unsaturation in the polymer.

This invention provides a bloom-inhibiting accelerator composition comprising a mixture of from about 25 to about 75 weight percent (preferably 25 to 50 wt. percent) of:

I. a thiourea of the structure i 1? Ti NC S CHQNHCNHCHQS CN and correspondingly from about 75 to 25 weight percent (preferably 75 to 50 percent) of a sulfur-containing compound selected from the group consisting of:

II. a polysulflde of the structure i II NCS CHzSxCHzS CN PW L V. the zinc salt of the reaction product of wsentially equimolar amounts of ethanolamine, formaldehyde and carbon disulfide; wherein the above structures R, R R and R are alkyl having one to eight carbon atoms or phenyl, R and R are alkyl having one to eight carbon atoms or phenyl, R and R are alkyl having one to eight carbon atoms, and each of R, R, R and R' taken together with the nitrogen atom to which they are attached can form a piperidino, pyrrolidino or morpholino radical, R and R are alkyl having one to eight carbon atoms,

and x is an integer of 2 to 6. (Of course, the total of the 1" component taken with the II, Ill, 1V, or V component in the composition will be percent).

The 1" compounds are known, being described in U.S. Pat. No. 2,068,355 to KL. Sibley. In the preferred embodiments R, R, R and R are alkyl of one to four carbon atoms.

The 1] compounds are described in the copending application of Harry E. Albert, Ser. No. 781,691, filed Nov. 29, 1968, now U.S. Pat No. 3,579,516, herein incorporated by reference. In the preferred embodiments the integer x is 2, and R, R, R and R are alkyl of one to four carbon atoms. Representative polysulfides embodied by the 11" compound designation are Bis[(N,N-dimethylthiocarbamyl)thiomethyl1disulfide Bis[(N,N-dimethylthiocarbamyl)thiomethyl1tetrasulfide Bis[(N,N-dimethylthiocarbamyl)thiomethyl]pentasulfide Bis[(N,N-diethylthiocarbamyl)thiomethyl1disulfide Bis[(N,N-diethylthiocarbamyl)thiomethyl1trisulfide Bis[(N,N-diisopropylthiocarbamyl)thiomethyljldisulfide Bis[ (N,N-oxydiethylene thiocarbamyl)thiomethylldisulfide Bis[(N,N-pentamethylenethiocarbamyl)thiomethyl]disul- Bis[(N,N-tetramethylenethiocarbamyl)thiomethyl]trisul- Bis[(N,N-dihexylthiocarbamyl)thiomethyl]disulfide Bis[(N,N-di-2-ethylhexylthiocarbamyl)thiomethyl]disulfide Bis[(N,N-dibutylthiocarbamyl)thiomethyl]trisulfide Bis[(N,N-diisobutylthiocarbamyl)thiomethylldisulfide (N,N-Dimethylthiocarbamyl)thiomethyl-(N',N'-

Diethylthiocarbamyl)thiomethyl disulfide Bis[(dialkylthiocarbamyl)thiomethyl]disulfide where alkyl is a mixture of methyl, ethyl and butyl, for example, the product prepared from equimolar amounts of dimethyl-, diethyl-, and dibutylamine Bis[(N-phenyl-N-methylthiocarbamyl)thiomethyl]disulfide Bis[(N-phenyl-N-ethylthiocarbamyl)thiomethyl1disulfide The 111" compounds, tetramethyl thiuram disulfide, i.e.

| (CHahN S S NKlHa):

and the mixture of at least 25 percent thereof with bis-(oxydiethylene)thiuram disulfide, i.e.,

S S N SSi JN are well known compositions.

The IV compounds are known and described in U.S. Pat. No. 3,308,103 to A.Y. Coran and E. Morita, herein incorporated by reference. In the preferred embodiments, R and R are alkyl of three to five carbon atoms and most preferred is zinc 0,0-dibutyl phosphorodithioate.

The V composition is described in terms of the zinc salt of the reaction product of essentially equimolar amounts of ethanolamine, formaldehyde and carbon disulfide because the molecular structure of said reaction product is not readily aseertainable.

The compositions of this invention, that is, the described mixture of the thioureal with any of the compositions, I], III, IV or V in the proportions as delineated, are employed as accelerators in the conventional manner in the vulcanization of elastomers, especially of ethylene-propylenediene (EPDM) elastomers. Generally in such vulcanizations from about 0.5 to 5 phr., preferably 1.5 to 4 phr., accelerator are used, generally with from about 0.5 to 3 phr. of sulfur as the vulcanization agent. (phr. means parts per hundred parts by weight of the elastomer). The accelerator composiu'on is milled into the elastomer along with the sulfur, and other optional modifying ingredients, for example, carbon black, stearic acid, zinc oxide, naphthenic oil and others known to the trade. The elastomer is then normally cured (vulcanized) by heating to from about 300 to 450 F. for from about seconds to 1 hour, usually for about 10-40 minutes at about 300-350 F.

It has been discovered that the mixed accelerators composition of the present invention not only retards blooming in the cured elastomer but also shows increased accelerator activity as demonstrated by a significant increase in elastomer tensile strength and modulus when comparisons are made at equivalent concentrations of accelerators and the same curing conditions. These improved results in acceleration activity and inhibition of blooming are noted for the claimed mixtures of the components compared to the equivalent concentrations of individual components used alone, as confirmed by the data presented hereinafter in Tables 1 3. Moreover, it has been found that the improvements are not obtained when thiourea I is mixed with other sulfur-containing compounds which are known accelerators and are similar in structure to the components of the mixture claimed, evidencing the unexpected results of the present invention (as confirmed, for example, by test Nos. ll, 24 and 25 of Table I, and tests 7 and 8 of Table 3). Similarly, improved results are not obtained when other thiourea compounds are substituted for the thiourea I of the present invention (see tests Nos. 29 and 30 of Table I, and tests 12 and 13 of Table 2).

The invention is illustrated and clarified, and the surprising results achieved by its practice are demonstrated, by reference to the following examples in which the preparation of various components is exemplified and the vulcanization evaluations of a representative EPDM elastomer using both claimed and comparative accelerator compositions are carried out. The following recipe is used, where the amounts of ingredients are based on parts by weight per hundred parts of elastomer.

Pans by weight EPDM elastomer (ethylene-propylene-dicyclopentadiene terpolymer) 100 Naphthenic oil 50 The curing of vulcanizate is carried out at 320 F. removing samples for testing at 5, 10, 2O, 30, 40 and 60 minutes intervals.

EXAMPLE 1: PREPARATION OF REPRESENTATIVE COMPOUNDS OF GROUP I A. At ambient temperature, 324 g. (4.0 moles) 37 percent formaldehyde solution is added to a mechanically stirred mixture of 152 g. (2.0 moles) thiourea, 1,000 ml. water and 517 g. (4.0 moles) dibutylamine. After dropwise addition of 318 g. (4.2 moles) carbon disulfide the reaction mixture is further stirred for 1 hour at elevated temperature (40-50 C.). After working up the reaction mixture, there are obtained 901 g. of crude product as viscous oil which slowly crystallizes on standing. Recrystallization of a portion of the crude product from chloroform-hexane mixture gives analytically pure product melting at 95-97 C., i.e.,

l ,3-bis[(N,N-dibutylthiocarbamyl)thiomethyl]thiourea,

B. Similar reaction of I29 g. (1.0 mole) diisobutylamine in 300 ml. water, 38 g. (0.5 mole) thiourea, 81 g. (1.0 mole) 37 percent formaldehyde solution and 76 g. (1.0 mole) carbon disulfide gives 197 g. of crude product as a viscous oil. Treatment of the crude product with methanol and subsequent crystallization from a benzene-hexane mixture gives a purified product melting at 1l7-120 C., l,3-bis[(N,N-diisobutylthiocarbamyl)thiomethyl]thiourea.

C. l,3-Bis[ (N,N-dialkylthiocarbamyl )thiomethyl1thiourea, where dialkyl" is mixed dibutyl and dimethyl, is similarly prepared by reacting 2 moles of a mixture of dibutyl and dimethyl amine with 1 mole thiourea, 2 moles formaldehyde and 2.1 moles carbon disulfide, in aqueous media.

D. The same thiourea as in part C is prepared, but with prereaction of the amines, formaldehyde and carbon disulfide as a first step, followed by addition of the thiourea as a second step.

EXAMPLE 2: PREPARATION OF REPRESENTATIVE COMPOUND OF GROUP II.

With stirring and moderate cooling, 1.57 moles hydrogen sulfide gas is absorbed in 3 moles of a mixture dimethylamine, diethylarnine and dibutylamine; 1.5 moles powdered sulfur is dissolved in the reaction mixture followed by 3 moles paraformaldehyde and then 3.3 moles carbon disulfide. The product is recovered as a brown oil, l,3-bis[(N,N-dialkylthiocarbamyl)-thiomethyl]disulfide, where dialkyl is mixed dimethyl, diethyl and dibutyl.

EXAMPLE 3: PREPARATION OF REPRESENTATIVE COMPOUND OF GROUP V.

Eighty-one grams of 37 percent aqueous formaldehyde solution is gradually added to a solution of 61 g. ethanolamine in 200 ml. water. The mixture is stirred 1 hour at 50-60 C. With cooling, 76 g. carbon disulfide is added and the mixture is stirred 2 hours at 4050 C. At room temperature the reaction mixture is then rapidly stirred into a solution of 144 g. zinc sulfate heptahydrate in 300 ml. water. The precipitated product is filtered, water-washed and air-dried to give a white powder which is the zinc salt of the reaction of ethanolamine, formaldehyde and carbon disulfide. The product decomposes if heated to -200 C.

EXAMPLE 4: VULCANIZATE EVALUATION.

Blooming The l" compounds and the II" compounds are evaluated alone as accelerators with regard to effect on surface-bloom characteristics in the vulcanization recipe previously described, and compared to mixed accelerator compositions wherein each l-compound is separately blended with the II- compound in proportions of 25 75 percent and 50 50 percent. In a series of tests, the recipes are adjusted so that 2, 3 or 4 phr of accelerator is used in conjunction with 2 phr sulfur; and 3,4 or 5 phr accelerator is used with 0.5 phr sulfur. The bloom evaluations are made in these tests 3 months after curing of the vulcanizates; results are reported in Table No. I. It is observed that the amount of surface bloom on the cured rubber when the mixed accelerators compositions are used generally ranges from none to light oil film or light crystal coating. However, when the individual accelerator compounds are employed alone in the recipe, the bloom of the rubber is significantly greater than that of rubber using corresponding concentrations of the mixed accelerator compositions, and heavy oil films and heavy crystal coatings are often observed on these single accelerator" vulcanizates. Accelerator Activity The relative accelerators activities in vulcanizates prepared using the accelerators and combinations thereof as abovedescribed is determined by measuring the tensile strengths and 200 percent modulus of the cured elastomers prepared from recipes using 2 phr. accelerator with 2 phr. sulfur, and 4 phr. accelerator with 0.5 phr. sulfur. At equivalent concentrations of ingredients, it is found that vulcanizates wherein the accelerator is the combination of components as claimed have significantly higher activities than when the individual components are used alone in the recipe. This is shown by markedly higher modulus values and tensile strengths of the vulcanizates, for example, as shown in Tables 2 and 3.

EXAMPLE 5 The foregoing tests and evaluations are carried out for other combinations of accelerators embodied within the invention and results compared to those obtained using the individual accelerator components alone. The results show marked decrease in surface bloom and significant increase in activity for the accelerator combination compositions of the invention. Comparisons are made with vulcanization recipes containing 2 phr accelerator with 2 phr sulfur, and 4 phr. accelerator with 0.5 phr. sulfur for the following accelerators wherein the group designation (Roman numerals) previously applied thereto is in parentheses.

Accelerator Composition a. 25% of thiourea (l) of Example 1 (A) and 75% of tetramethyl thiuram disulfide (Ill) test No. 21 of Tabl .1

test 15 of Table l and test 9 of ..Tl ls2 a...

b. 25% and 50% of thiourea (I) of Example 1 (A) and 75% and 50%, respectively, of polysulfide (ll) of Example 2 c. 25% of thiourea (l) of Example 1 (C) and 75% of zinc 0,0-dibutyl p p nmoae x) test 26 of Table l and test 8 Q I fl l tests 22 and 23 i of Table l and test 5 of of Table 3 V e. 25% of l,3-bis[(diethylthiocarbamyl)- test 19 of Table l -thiomethyl] thiourea (I) and 75% of bis [(dibutylthiocarbamyl)- t hy l el ds 1) and test 6 of Table 3 f. 25% of thiourea (l) of Example 1 (D) and 75% of polysulfide (II) of test 28 of Table l Example 2 V n A h N a MW g. 50% of thiourea (l) of Example I test 27 (A) and 50% of zinc salt (Example 3) of Table l and of reaction product of ethanolamine, test 7 of formaldehyde and carbon disuflide (V) Table 2 h. the compositions set forth as tests 1B amal a i. the compositions set forth as tests 10 and 11 of Table 2.

EXAMPLE 6 (a) 50% of thiourea (I) of Example 1 (C) and 50% of polysulfide 0f the structure 8 Test 24 of Table 1. 5 II II RZNCSSONRZ Where R, is

mixed dimethyl and diethyl.

(b) 33% of thiourea (I) of Example 1 Test 25 of Table 1, and (lggtaps'fiZ, o1 polysulfide of f Test 8 of Table 3 10 (e) 75% of polysulfide (II) of Example 2, and 25% of thiourea Strucmm Test of Table 1, and

S Test 12 of Table 2. ll (C4H0NHONH) C411 (d) 75% of polysullide (II) of Example 2, and of 3:2 mixture of thiourea of the structure 20 Test of Table 1, end

(O Hi)NHCNH(C H and the Test 13 Table thiourea of the structure ll (C2H5)NHCNH(C2H5) 25 m 24* V. A. H, c.

TABLE I Bloom on EPDM vulcanizete 30 2 phr. ac-

celerator, 4 phr. 2 phr. aeeel. Accelerator sulfur. 0.5 phr. S.

See Example l-A N one Heavy. See Example 1-B Medium. 3 amp Do. Do. Do. Heavy Do. Light. Heavy t Do. [O(CHzCHz)2NC(S)S]z. 3 arts of N0. 9 plus 1 part Heavy Do.

C2HB)2NC(S)S]2. [(C4Hn0);P(S)S]2Zn Light- Medium. See Example 3 .do.--. Light. 1 part of No. 1 plus 1 part of No. 6. None. None 22 I: lpsrt of No.3pluslpart oINo. 23 1 part of No. 3 plus 3 parts of No.

24 l pert of No. 3 plus 1 part of No. 25 1 part of No. 3 plus 2 parts of No.

11. 26 1 part of N0. 3 plus 3 parts of No.

1 27 1 part of No. 1 plus 1 part of No.

28 1 pal-t of No. 5 plus 3 parts ofNo. ..do Do. 29 3 parts 01 No. 6 ins 1 part of Heavy Heavy.

(C4 eN )2C 30 3 parts of No. 6 plus 0.5 pert of do Do.

(C2H5NH)2C (S) and 0.5 part of 4 nN )2 TABLE 2 Vulcenlzete; acceL-4 phn; sull'ur0.5 phr.

Tensile (p.s.i.) Modulus, 200% at cure time (p.s.i.) at cure time ofof Test 10 20 40 10 20 40 No. Accelerator min. min. min. min. min. min.

1 See Example l-C 1,230 1,480 1,610 430 550 620 2. See Example l-A ,250 1,650 1,860 450 550 640 3. See Example l-li 750 1,430 l, 700 350 580 660 4 See Example 2 1, 1,650 1, 750 450 660 600 5 [(C4H9OQP(S)S]2ZIL 050 1, 500 1, 750 6". See Example 3 1, 300 1, 600 l, 620 600 700 710 TABLE 2 Continued Vulcanizato; 00001.4 phr.; sullur0.5 phr.

Tcnsilo (p.s.i.) Modulus, 200% at cure time (p.s.i.) at cure time olof- Test 10 20 40 10 20 40 No. Accelerator min. min. min. min. min. min.

7 1 part of No. and 1 part of No. 2 1,860 2,020 1,960 740 825 800 8 3 parts of N0. and 1 part ofNo.1 1,300 1,700 1,800 0... 1 part of No. 2 and 1 part of No. 4.

0 1,430 1,830 1,010 500 660 700 10.. 1 part of No. 3 and 1 part of No. 4 1,420 1,750 1,060 500 580 080 1 part of N0. 1 and 3 parts of No. 4 1,670 1, 950 2, 060 640 730 840 12.- 3 parts of No. 4 and 1 part of (CiHqNlI)gC(S) 060 1, 570 1, 640 400 540 550 13"... 3 parts of No. 4, 0.5 part of (C4H5NH)C (S), and 0.5 part of (CzHaNI 890 1, 550 1, 650 350 520 550 TABLE 3 Vulcanlzate; accel.2 phr.; sulfur-2 phr.

Modulus, 200% 'lnnsllu (p.s.l.) m, (00.1.) at cum cure time 0l'--- time 01'- 'lvsiv 10 20 40 number Accelerator min. min. min. min. min. min

1 .1 See Example 1-0 2,020 2, 550 2, 750 750 1,050 1,340 2 [(CzH5)zNC(S) H2NH]2C(S) 2,260 2,500

3 [(C1H)2NC(S)SCH1S:} 2,025 2,400 825 1,175

4 3parts of [O(CH2CH2)2NC(S)S3- 811111 part O [(CHs)2NC(S)S: -l 1,220 2,150 2,500 450 760 1,150

5 1 part of No. 4 and 1 part of N0. 1 2,070 2,710 2,730 770 1,250 1,470 6 1 part of No. 2 and 3 parts of N0. 3 2, 240 2,600 900 1, 250

7 3parts of|:(CH;)zNC(S)S and 1 part of 2H5)2N (S)S; .1 2,180 2, 540 2,770 870 1, 350 1,540

8 2 a1-ts oiNo. 70110 1 part of N0. 1 2,150 2,550 2,725 850 1,250 1,560

We claim: R90 S 1. A surface bloom-inhibiting vulcanization accelerator 40 s-Zn and compos1t1on compnsmg a mixture of from about 25 to about 75 weight percent of R 0 2 I. a thiourea of the structure V. the zinc salt of the reaction product of essentially R S S s R: equimolar amounts of ethanolamine, formaldehyde and H H II carbon disulfide; where in the above structures R, R, R NCsCHzNHCNHCHZsCN and R are alkyl having one to eight carbon atoms or R2 phenyl, R and R are alkyl having one to eight carbon "j atoms or phenyl, R and R are alkyl having one to eight and correspondingly from about 75 to 25 weight percent of carbon atoms, and each of 5 6 7 and s taken Sulfur-Containing compound Selected from the group together with the nitrogen atom to which they are atconsisting of: tached can form a piperidino, pyrrolidino or morpholine IL A Polysulfide ofthe stmctm'e radical, R and R are alkyl having one to eight carbon atoms, and x is an integer of 2 to 6. R S S R 2. The composition according to claim 1 where component H H l is 25 to 50 percent of the mixture.

H N No S OHzs 2s 0 3. The composition according to claim 1 where R, R R, m R, R", R, R and R are alkyl of one to four carbon atoms,

- Y and R and R are alkyl of three to five carbon atoms. tetramethyl thiula-m disulfide, a mixture of 4. The composition according to claim 3 wherein the intetramethyl thiuram disulfide and bis(oxydiethylene)thiuteger x t t e II) i 2, ram disulfide containing at least about 25 percent by 5. The composition according to claim 3 where R and R weight of tetramethyl thiuram disulfide; are butyl. IV. a zinc phosphorodithioate of the structure 

2. The composition according to claim 1 where component I is 25 to 50 percent of the mixture.
 3. The composition according to claim 1 where R1, R2, R3, R4, R5, R6, R7 and R8 are alkyl of one to four carbon atoms, and R9 and R10 are alkyl of three to five carbon atoms.
 4. The composition according to claim 3 wherein the integer x (structure II) is
 2. 5. The composition according to claim 3 where R9 and R10 are butyl. 